the Salon.com Web site, which contains a wide range of news and cultural commentary,

as  Sex, Profanity,  based on the fact that the site includes a regular column that deals

with sexual issues.

Blocking by both domain name and IP address is another practice in which

filtering companies engage that is a function both of the architecture of the Web and of

the exigencies of dealing with the rapidly expanding number of Web pages.  The category

lists maintained by filtering software companies can include URLs in either their human 

readable domain name address form, their numeric IP address form, or both.  Through

 virtual hosting  services, hundreds of thousands of Web sites with distinct domain

names may share a single numeric IP address.  To the extent that filtering companies

block the IP addresses of virtual hosting services, they will necessarily block a substantial

amount of content without reviewing it, and will likely overblock a substantial amount of

content.  

Another technique that filtering companies use in order to deal with a structural

feature of the Internet is blocking the root level URLs of so called  loophole  Web sites. 

These are Web sites that provide access to a particular Web page, but display in the

user's browser a URL that is different from the URL with which the particular page is

usually associated.  Because of this feature, they provide a  loophole  that can be used to

get around filtering software, i.e., they display a URL that is different from the one that

appears on the filtering company's control list.   Loophole  Web sites include caches of

Web pages that have been removed from their original location,  anonymizer  sites, and

65